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Tropical Storm LEE (Text)

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TROPICAL STORM LEE DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
400 PM CDT SUN SEP 04 2011
 
WSR-88D RADAR DATA AND SATELLITE IMAGERY INDICATE THAT LEE HAS
BECOME A LITTLE BETTER ORGANIZED EVEN THOUGH THE CENTER IS WELL
INLAND NOW OVER SOUTH-CENTRAL LOUISIANA. OTHER THAN THE STRONG
BURST OF DEEP CONVECTION THAT HAS DEVELOPED NEAR THE SURFACE
CENTER...NARROW BANDS OF MODEST CONVECTION CONTINUE TO FORM OVER
SOUTHEASTERN LOUISIANA AND NEAR THE FLORIDA PANHANDLE...WHICH EXTEND
SOUTHWARD OVER THE GULF OF MEXICO FOR A COUPLE HUNDRED MILES. SOME
OF THESE BANDS HAVE CONTAINED DOPPLER VELOCITIES OF 60-68 KT FROM
4500-10000 FT IN 25-35 DBZ ECHOES...WITH MEAN VALUES OF ABOUT 55
KT. ALTHOUGH THESE DOPPLER VELOCITY VALUES WOULD TYPICALLY
TRANSLATE TO SURFACE WINDS OF 45-50 KT...THE WEAK ECHO RETURNS
SUGGEST THAT HIGHER WIND SPEEDS WILL MAINLY OCCUR IN GUSTS. THE
INITIAL INTENSITY IS BEING MAINTAINED AT 40 KT BASED ON SUSTAINED
WIND REPORT OF 40 KT FROM THE BURAS C-MAN STATION...AND THE GUST
DIFFERENTIAL IN THE FORECAST/ADVISORY PRODUCT REMAINS AT 55 KT...
WHICH IS A LITTLE HIGHER THAN THE STANDARD 50-KT GUST VALUE IN
ORDER TO ACCOUNT FOR THE TRANSIENT STRONGER WINDS ALOFT NOTED IN
DOPPLER VELOCITY DATA.
 
LEE HAS BEEN MOVING TO THE NORTH OVER THE PAST 6 HOURS. HOWEVER...
THE CYCLONE IS EXPECTED TO SLOW DOWN AND TURN TO THE NORTHEAST OR
EAST-NORTHEAST WITHIN THE NEXT 6 TO 12 HOURS. OTHERWISE...THERE IS
NO SIGNIFICANT CHANGE TO THE PREVIOUS TRACK FORECAST REASONING. A
VIGOROUS SHORTWAVE TROUGH OVER THE NORTHERN AND CENTRAL PLAINS IS
EXPECTED TO CONTINUE DIGGING SOUTHEASTWARD AND GRADUALLY LIFT OUT
TO THE NORTHEAST AT A SLIGHTLY FASTER FORWARD SPEED. BY 36 HOURS...
A PIECE OF ENERGY FROM THE SHORTWAVE IS FORECAST BY ALL OF THE
MODELS TO BREAK OFF AND BECOME ABSORBED INTO THE CIRCULATION. THIS
MID-LEVEL BAROCLINIC INTERACTION...COUPLED WITH ABSORPTION BY A
FRONTAL SYSTEM...IS EXPECTED TO TRANSITION LEE INTO A LARGE
LOW-LATITUDE EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE TENNESSEE
VALLEY BY DAYS 2-4. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE
PREVIOUS ADVISORY AND CLOSELY FOLLOWS THE CONSENSUS TRACK MODELS...
TVCN AND TVCA.
 
ALL OF THE GLOBAL AND REGIONAL MODELS ARE NOW FORECASTING LEE TO
REMAIN A TROPICAL STORM OR EXTRATROPICAL GALE AREA FOR THE NEXT 36
HOURS OR SO AS THE CYCLONE GETS A SHOT OF BAROCLINIC ENERGY FROM AN
UPSTREAM SHORTWAVE TROUGH. THIS TREND WAS FOLLOWED IN THE OFFICIAL
INTENSITY FORECAST...AND IS A BLEND OF THE INTENSITY CONSENSUS
MODEL ICON...AND INPUT FROM THE NHC TAFB UNIT.
 
SINCE HEAVY RAINS...STRONG WINDS...AND THE HIGHEST STORM SURGE
VALUES ARE OCCURRING VERY FAR FROM THE CENTER...IT IS IMPORTANT NOT
TO FOCUS ON THE EXACT LOCATION OF THE CENTER OF LEE. THE PRIMARY
THREAT FROM LEE WILL BE EXTREMELY HEAVY RAINFALL OVER MUCH OF THE
SOUTHEASTERN U.S. DURING NEXT SEVERAL DAYS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/2100Z 30.6N  91.8W   40 KT  45 MPH
 12H  05/0600Z 30.7N  91.0W   35 KT  40 MPH...INLAND
 24H  05/1800Z 31.2N  89.6W   35 KT  40 MPH...INLAND
 36H  06/0600Z 32.3N  88.3W   35 KT  40 MPH...POST-TROP/EXTRATROP
 48H  06/1800Z 33.3N  87.5W   30 KT  35 MPH...POST-TROP/EXTRATROP
 72H  07/1800Z 34.8N  86.8W   20 KT  25 MPH...POST-TROP/EXTRATROP
 96H  08/1800Z 36.0N  86.8W   20 KT  25 MPH...POST-TROP/EXTRATROP
120H  09/1800Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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